The invention relates to a process for the preparation of an aromatic hydrocarbon mixture from a monoolefin with at most 4 carbon atoms in the molecule (a C.sub.4 - monoolefin) or from a hydrocarbon mixture which consists of more than 75%w C.sub.4- monoolefins, using a certain crystalline silicate as the catalyst.
In an investigation by the applicants concerning the above-mentioned process it has been found that the aromatics selectivity and the change of this selectivity of these catalysts with time are in the first place greatly dependent on the value of y in the formula appearing hereinafter, where y is the alumina to silica ratio, which gives the overall composition of the silicate, and further on the average crystallite size (d) of the silicate. It was ascertained that to reach an aromatics selectivity and a change of this selectivity with time which are acceptable for commercial use of the process, y should be at least 0.0030 and at most 0.0075, and d at most 500 nm.